Don't know if this is 6.4 related or not, but I've noticed that since threadsdev upgraded to 6.4 any post I haven't read stays unread.
For example, I don't read all the modifications posts, but I have many that are listed as unread going back a couple weeks... Meant to ask about this before, is this a new feature in 6.4? Or a handy bug for me?
Maybe that's what you were looking for Gardener?